It has been shown that radioimmunoassay (RIA) methods are much superior to other analytical techniques for quantitation of steroid hormones in body fluids. However, at the present time direct determination of these hormones is still not possible and prior chromatographic separation of interfering steroids is necessary in most cases. It is desirable to develop highly specific antisera and RIA methods for a variety of steroids because it provides us with capabilities to study intracellular localization of these hormones in target tissues and their secretion and metabolism under both physiological and pathological conditions. The objective of the present investigations is to synthesize new and conformationally favorable steroid haptens for covalent linkage with protein carriers and to develop highly specific, sensitive and rapid RIA methods for the following steroids: Estrogens used in oral contraceptives, namely 17 alpha-ethynylestradiol and mestranol; androgens consisting of testosterone, dehydroepiandrosterone, etiocholanolone and other metabolites of testosterone; and in the corticosteroid group hydrocortisone will be included in the study. For obtaining highly specific antisera for steroids having 4,5 or 5,6 double bond it is preferable to link the steroid to protein through ring C at C-11 position and for steroids with 5 alpha-conformation it is desirable to couple through the C-19 or C-18 methyl groups from the top side (beta-side).